A flat serve hit with deadball might be considered a "topspin" serve, like a knuckleball in baseball. Low rackethand at trophy, finish after ball strike with a high hand and high elbow when the racket is pointing straight down at the ground.
The normal top/slice second serve uses some amount of pronation, but since most players hold the grip more backhand than for flat serves, the pronation never hits the ball flat. Ball toss is over your head, so the racket is angled, not pointing straight up at the sky. The angle allows you to swing up and over the ball, giving the topspin.

There's less pronation, or perhaps it is better to say that the timing of the pronation is different on a topspin serve. The pros usually turn more away from the court and the racket path is more across than toward the target. The racket still lags meaning that pronation (internal shoulder rotation) is need to turn the racket face to the ball, but it occurs later in the swing because the shoulder usually aren't turned as much forward. Topspin is also due to impacting the ball at a slightly lower level and more to the left.

The topspin serve needs a horizontal component like any other serve and the pronation (internal shoulder rotation) is what adds a lot of that juice.

The way to get spin with pronation is to make sure you pronate UP and OUT. Look at the picture of Pete Sampras at maximum pronation. His elbow is above his head and away from his body. He got more pronation and hit more spin on first and second serves than anybody. People who pronate but can't get spin most likely have their elbow around eye level and close to their body in this position. Look at yourself in the mirror in this position. Is your elbow up and out? If the picture doesn't show up in the post, the link is http://www.tennisserver.com/turbo/images/turbo_03_12/Sampras7.jpg.

I been trying the Salzsenstein version. For me to get the maximum forward spin and highest bounce it seems to be best to hit the topspin serve without any pronation just as he said. If you add some pronation you can get the ball to move forward faster and bounce a little bit sideways but lose some bounce height. It is also more strain on the elbow for sure.

There's less pronation, or perhaps it is better to say that the timing of the pronation is different on a topspin serve. The pros usually turn more away from the court and the racket path is more across than toward the target. The racket still lags meaning that pronation (internal shoulder rotation) is need to turn the racket face to the ball, but it occurs later in the swing because the shoulder usually aren't turned as much forward. Topspin is also due to impacting the ball at a slightly lower level and more to the left.

The topspin serve needs a horizontal component like any other serve and the pronation (internal shoulder rotation) is what adds a lot of that juice.

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As I've pondered this subject over the past year or so, I've come to a nearly identical conclusion. That is, the "later" pronation, the more "sideways" racket path, the lower and more "to the left" contact yielding the topspin.

Hadn't thought about the difference in the shoulder turn, but that makes a lot of sense, too, and maybe helps explain why even some of the better local women players can't hit the topspin serve, and often bring that right foot over to the right of the left in their "pinpoint" service motions.

I don't think that pronating "precludes" the snapping of the wrist in that sort of combo "flexion-ulnar deviation" that causes the racket to accelerate in the plane of the string-bed for maximum spin. But, if I *do* concentrate on the pronation aspect, while I get more pace, the bounce is lower and significantly less aggravating to many opponents. *And*, my margin for error over the net drops significantly.

Somewhere just before 0:08, when Stosur has her arm straight and up, she forcefully and rapidly uses internal shoulder rotation (or upper arm rotation) best seen by the elbow bones rotating. ISR occurs as the racket goes from about 90° to the straight arm and with the racket 'edge on' toward the ball to an angle called β at impact (shown in the thumbnail).

See ISR and β on all the other Vimeo serves showing the view from behind the server. β is the racket angle at impact shown on all thumbnails.

Leading up to β at impact the racket must be at an angle (~90° to β) to the arm to develop racket head speed from the straight arm rotation provided by ISR. Notice at impact that the strings are still going up for topspin even though she is near the top of her swing path.

In the later part of her follow through you see strong pronation that is necessary because the arm and racket are rotating and translating so fast that pronation is necessary to reduce stress stopping the motion and avoid injury.

This sequence of motions is complex and I have never seen it described in its entirely by words. I believe that you need words and high speed video together.

To video this rapid motion and the racket and ball at impact requires high speed video and a fast shutter speed.

Term Usage - Internal Shoulder Rotation and Pronation. The term 'pronation' is widely used for tennis discussions in a way that is not definable:
1) by searching on the internet
2) by tennis instructors
3) by any forum readers

As I've pondered this subject over the past year or so, I've come to a nearly identical conclusion. That is, the "later" pronation, the more "sideways" racket path, the lower and more "to the left" contact yielding the topspin.

Hadn't thought about the difference in the shoulder turn, but that makes a lot of sense, too, and maybe helps explain why even some of the better local women players can't hit the topspin serve, and often bring that right foot over to the right of the left in their "pinpoint" service motions.

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FuzzyYBs has an excellent video on how to hit a topspin serve that includes a slow motion video taken from above the same server hitting a first and second serve. This clearly demonstrates the shoulder turn and difference in racket path. The first serve is more toward the target and the second serve the server turns more away from the ball and across. At contact the shoulders are less square to the target. Just doing this will put more spin on the ball.

the problem with technology is there is too much over analysis. go out there and try to throw with the racket (but dont really throw it) upward. its best to just get a lesson so someone can show you in person. no amount of text/youtube can replace a good lesson

im trying to learn to pronate, but i can't imagine how to get topspin.seems like pronating just helps you hit a super fast flat serve.

where exactly during the serving motion is the strings brushing up on the ball, before the pronation?

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I'm with the folks who are not-so-big on all this lingo, but don't get me wrong - I'm absolutely on your side as far as developing a topspin serve.

Here's the thing: unless you elbow yourself good 'n hard in the stomach when you hit your flat serve, congratulations, you have pronation! That particular action is really a result of other things - those "things" are the deliberate actions that are where you want your focus. With the right setup, grip, toss location, swing path, contact point, etc., you'll get that topspin going just fine. Stay patient though.

One tricky aspect of getting topspin on that serve is that we need to catch the ball before the racquet tops out - that's not so easy when we have a flat serve as a reference. To make some topspin (for a right-hander), the contact point with the toss is usually slightly lower and also slightly more to the left, the swing path may be more left-to-right, and a grip position shaded a bit more toward eastern backhand may also help.

This is a pretty significant to-do list. Instead of "throwing" the racquet through the back of the ball to drive a flat serve toward the target, hitting with topspin means learning to "throw" the racquet upward through the ball. Instead of swinging right toward the target, a topspin serve uses more angular contact to send the ball toward a target. Building that instinct will take some deliberate practice.

In the mean time, keep your arm good 'n loose - it will pronate on its own if the other things are going right.